1 Pure water system workflow and influencing factors
1.1 Raw water pretreatment Raw water refers to the tap water that enters the laboratory. Pretreatment is to remove most of the impurities in the tap water.
1.1.1 Method: Pretreatment generally uses mechanical filtration, which is carried out in three steps:
①Precision filter element (also known as filter element, wire wound filter element and melt blown filter element) filter large particles such as sand and sand in the raw water;
②The activated carbon filter element removes most of the organic matter and heavy metal ions in the water by adsorption (especially the residual chlorine in the tap water, which has a great oxidation effect on the reverse osmosis membrane, so it must be removed by activated carbon);
③Reverse osmosis membrane (RO) further removes microscopic particles and salt in the water.
1.1.2 Influencing factors:
①Tap water quality: High impurity content in tap water will shorten the service life of pretreatment components and substandard water quality after treatment, and even block the pipeline, resulting in higher inlet pressure to work. Generally, the content of dissolved solids in tap water is required ( TDS) is less than 200 mg/L.
②Service life of pretreatment components: precision filter element, activated carbon filter element, reverse osmosis membrane, etc. are all materials with a relatively long life. Among them, the precision filter element and activated carbon filter element have a protective effect on the reverse osmosis membrane. If they fail, the load on the RO membrane will increase. , The life span will be shortened. Because the quality of the products of each manufacturer is different, and the RO membrane is expensive, in actual use, it should be used reasonably according to the quality of tap water in various places.
③Inlet water pressure: Generally, the pretreatment of pure water system requires a high-pressure pump to maintain a certain inlet pressure (≥0.1Mpa) to maintain normal operation. When the pressure of the high-pressure pump is insufficient, the water production will decrease.
④Maintenance of the pure water system: the pure water system generally has an automatic backwashing function. When its setting is unreasonable or faulty and manual maintenance is not correct, it will also affect the normal operation of the pure water machine, resulting in a decrease in purification efficiency and water quality.
1.2 Preparation of deionized water The general pure water system is limited by cost and the quality of RO membrane is average, and the water treated by it can only reach the standard of tertiary pure water (resistivity> 0.2MO.cm). Although the tertiary pure water has been pretreated to remove most of the ions, the ion concentration in it is still high, which will also affect the trace detection of the biochemical analyzer. Therefore, the tertiary pure water must be further deionized to achieve the first pure water (Resistivity ≥ lOMΩ.cm) standards can be used for biochemical testing.
1.2.1 Method: The ion exchange resin method is a common method for the preparation of deionized water. The component used is the ion exchange column or purification column (tank), including anion exchange column, cation exchange column and mixed column, etc. The reagent is anion and cation exchange. Resin. Anion and cation exchange resins are generally polymerized from styrene and then cross-linked by divinylbenzene to obtain a porous network skeleton structure, and then active groups are connected to the skeleton to form a high molecular polymer. The active groups connected to ion exchange resins can be divided into two types: acidic groups and basic groups. Ion exchange resins connected with acidic groups are called cation exchange resins, and resins connected with basic groups are called anion exchange resins.
1.2.2 Principle:
①The principle of the cation exchange column is the principle of hard water softening: the acidic groups in the cation exchange resin include sulfonic acid groups (-S03H), carboxyl groups (-COOH) and phenol groups (-C6H40H), among which hydrogen ions can interact with The metal ions or other cations in the solution are exchanged. For example, the high polymer of styrene and divinylbenzene is sulfonated to obtain a strong acid cation exchange resin. Its structural formula can be expressed as R-SO3H, where R represents the resin matrix, taking Ca2+ as an example, the expression is 2R-S03H+ Ca2+ -(R-SO3 )2Ca+ 2H+.
②The principle of anion exchange column: the basic groups in anion exchange resin include quaternary amine groups [-N (CH3)30H], amine groups (-NHz) and imino groups (-NHz). They can generate OH- ions in water and can exchange with various anions. Taking Cl- as an example, the expression is R-N (CH3)30H+Cl-RN(CH3)3Cl+OH-.
